1. Field of Invention
The present invention relates to a guide plate, a surface light source device of side light type and a liquid crystal display; in particular, the invention relates to a guide plate improved so as to prevent sheet members such as prism sheet from sticking to an emission face of the guide plate, and still relates to a surface light source device of side light type as well as to a liquid crystal display (LCD) which employs the improved guide plate.
2. Related Art
It is a well-known technique to apply a surface light source device of side light type to devices such as LCD comprising a LCD panel illuminated by the light source device. This arrangement is suitable for thinning the overall shape.
The surface light source device of side light type comprises generally a rod-shaped light source such as fluorescent lamp as primary light source, which is disposed besides a guide plate (plate-like guide). Illumination light emitted from the primary light is introduced into the guide plate through an end face (incidence end face). Thus introduced light propagates within the guide plate and brings meanwhile emission from a major face (emission face) of the guide plate toward the LCD panel.
Known guide plates which are employable in surface light source devices of side light type includes ones having substantially uniform thickness and others having tendency to decrease thickness according to distance from a primary light source. In general, the latter emits illumination light more effectively than the former.
It is well known that various sorts of sheet members are employed to be arranged along an emission face of a guide plate. A prism sheet being arranged, emission directivity of the guide plate is corrected. A light diffusion sheet may be arranged in order to scatter emission from the guide plate weakly so that various processed portions of the guide plate are hardly conspicuous.
These sheet members are apt to stick to the emission face because of factors such as static electricity. In particular, a case such that a prism sheet is disposed on an emission face will lead to a serious problem. The problem is illustrated in FIGS. 13 through 15.
In general, sticking of a prism, sheet occurs so that some parts of the sheet contact adhesively with the emission face. Thus a resultant condition will involve a state as illustrated in FIG. 13 and another state as illustrated in FIG. 15. In the former state, tops of projections 1A of a prism sheet 1 stands apart from an emission face 2 of a guide plate 2, with an air layer being interposed. Accordingly, this state provides no light path which leads to the projections 1A from the guide plate 2 directly without passing through the air layer.
On the other hand, in the latter state, tops of projections 1A of the prism sheet 1 contact with the emission face 2 of the guide plate 2. Accordingly, this state provides a lot of light paths which lead to the projections 1A from the guide plate 2 directly without passing through the air layer. Illumination light going on such paths will produce local high brightness portions on an outer face of the prism sheet 1.
This causes bright-dark pattern M to appears and to be visible from the outside of the prism sheet 1 as illustrated in FIG. 13. It is needless to say that such bright-dark pattern reduces quality of illumination. Further, application to backlight in LCDs leads doubtlessly to reduction in quality of display.
The present invention has been proposed under the above described background. An object of the present invention is to provide a guide plate improved so that a sheet member such as prism sheet does not stick to an emission face. Another object of the present invention is to provide a surface light source device of side light type employing the improved guide plate to avoid quality of illumination from being reduced. And still another object of the present invention is to provide a liquid crystal display employing the improved surface light source device of side light type to avoid quality of display from being reduced.
First, the present invention is to be applied to a guide plate comprising an emission face for light-output, a back face and an incidence end face for light-input. According to a fundamental feature, the emission face is provided with a plurality of projections each of which includes a blunt top portion. The improved guide plate prevents a sheet member such as a prism sheet disposed on an emission face from sticking and avoids the sheet member from being damaged.
According to a typical embodiment, the projections are domed. The dome-like shape is featured by being provided with a blunt top portion. Each dome-like projection has a diameter preferably falling within a range from 50 xcexcm to 200 xcexcm and has a height preferably falling within a range from 0.1 xcexcm to 50 xcexcm. The dome-like projections distribute preferable with density such that at least one projection is allocated per box of 0.5 mmxc3x970.5 mm.
According to another typical embodiment, ridge-like projections each of which includes a blunt ridge-top portion are employed. Each of the ridge-like projections runs crosswise with respect to the incidence end face. Whereas a preferable crossing angle is not less than 60 degrees, a typical crossing angle is 90 degrees,
Ratio of repetition pitch of the ridge-like projections to their height preferably falls within a range from 5000:1 to 1:1. And height of each ridge-like projection preferably falls within a range from 1 xcexcm to 100 xcexcm.
In every embodiment, the emission face may be further provided with light scattering pattern consisting of a plurality of light diffusion elements to scatter illumination light. Such scattering pattern not only promotes emission from the emission face but also additionally prevents the sheet member from sticking.
The present invention is also to be applied to a surface light source device of side light type including a primary light source, a guide plate supplied with light from the primary light source and a sheet-like member, the id guide plate comprising an emission face for light-output on which the sheet-like member is disposed, a back face and an incidence end face for light-input. The aforesaid improved guide is employed. Thus employed guide plate allows the above embodied styles, enabling accordingly a sheet member such as a prism sheet disposed on an emission face to avoid sticking and damage. As a result, reduction in quality of illumination is avoided.
Further, the present invention is to be applied to a liquid crystal display including a liquid crystal display panel and a surface light source device of side light type to illuminate the panel. It should be noted that the above improved surface light source device of side light type is employed for illuminating the LCD panel. This surface light source device of side light type employs the above guide plate which allows the above embodied styles, enabling accordingly a sheet member such as a prism sheet disposed on an emission face to avoid sticking and damage. As a result, reduction in display quality of the LCD is avoided.
The present invention is further described in detail with referring to the accompanied drawings. It is to be noted that the drawings contain some exaggerated illustration for the sake of easy understanding.